Adventures in Fractal's Dual Rectifiers

[dk_ace]

Here's our OG Dual Rec into a real cabinet compared with the model into the appropriate SIC:

View attachment 15395

Green is the amp, blue is the Axe-Fx.

On the amp the MV is around 9 o'clock (as loud as I dared to go and not get divorced). I had to set the model to 1.2 to get the same response. Above that and the power amp starts clipping and the highs get reduced. This is to be expected given the different taper between the amp and the model.

Cool. This thread surprised me, as I always thought the fractal recto models were accurate to my experiences with my own amp.

Obviously @MirrorProfiles was having a different experience with his from the clips.

D

 

[Mongillo19]

Cool. This thread surprised me, as I always thought the fractal recto models were accurate to my experiences with my own amp.

Obviously @MirrorProfiles was having a different experience with his from the clips.

D

I didn't realize how much the high treble adds that sizzle. I believe Mirror tried that but still Ive never touched it before

 

[FractalAudio]

@FractalAudio
.mdat (REW)

https://drive.google.com/file/d/1CIXnHKG8nak7QItTsvOy8KSMvc1GytvG/

Needs to be a text file. That's a binary file. Like this:

* Measurement data measured by REW V5.20.13
* Source: Universal Audio Thunderbolt, Universal Audio Thunderbolt, 2, volume: no control
* Format: 256k Log Swept Sine, 1 sweep at -12.0 dBFS, at 44100 Hz
* Dated: Nov 12, 2023 8:22:54 PM
* Sense Resistor: 100.0
* Lead resistance: 0.000
* Input resistance: 20000.000
* Calibration factor: 0.8760
* Note: ;
* Measurement: Nov 12
* Smoothing: None
* Frequency Step: 0.3364563 Hz
* Start Frequency: 1.0 Hz
*
* Freq(Hz) Z(Ohms) Phase(degrees)
2.018738 6.388672 2.8574
2.355194 6.392652 3.2260
2.691650 6.397457 3.6134
3.028107 6.401032 4.0127
3.364563 6.406793 4.4147
3.701019 6.413116 4.8179
4.037476 6.418531 5.2077

 

[James Freeman]

Got it.
You say it has to also be as close to DC as possible?

 

[FractalAudio]

Got it.
You say it has to also be as close to DC as possible?

If you can't get below, say, 20 Hz then I need the DC resistance as well. Ideally below 20 Hz and the DC resistance.

 

[James Freeman]

Exported as text starting from 1Hz.
At 400Hz 14.5 Ohm, at 5Hz 12.5 Ohm.

https://drive.google.com/file/d/1GCgxTRQn0hHvL4Od6nqkdAAiseB8N3ld/

 

[la szum]

What revision Dual Rectifier:
The one with the 1M gain pot instead of 250K?
The one with the 100K presence pot or the one with 25K?
The one with the bright cap on the master volume or maybe one with the treble bleed to ground on the MV?
Or maybe one of the ones with a 220pF plate cap on V2B instead of 1nF?

There have been so many changes over the years to these things. Mesa denies changing anything but their own schematics as well as "people in the know" say differently. Randall was always tinkering with the circuit. Later revisions were darker to try to tame the fizz that people complained about. But then people said they were muddy so more changes ensued.

I'll drag our reference Dual Rec. out tomorrow and measure it but I doubt it's off by much.

Do you ever get exhausted with people referring to "Amplifiers" as if they are these
monolithic creatures that existed in one ideal, frozen state, with zero variability?

I can only imagine.

 

[la szum]

This thread is PURE GOLD! Thank you all.

I feel like I need to fill some Pints up and bring in some Tapas.

 

[DrewJD82]

This thread is PURE GOLD! Thank you all.

I feel like I need to fill some Pints up and bring in some Tapas.

Just shave your legs before you put the skirt on this time, I had a hard time sorting myself out last time.

 

[la szum]

 

[la szum]

So are the takeaways that no 2 Rectos were ever created equal; and that low Master Volumes
on the Models in the Fractal are needed to more accurately approximate the behavior
of the Actual Amps themselves??

That and a dozen other things I probably am not smart enough to notice.

 

[FractalAudio]

Exported as text starting from 1Hz.
At 400Hz 14.5 Ohm, at 5Hz 12.5 Ohm.

https://drive.google.com/file/d/1GCgxTRQn0hHvL4Od6nqkdAAiseB8N3ld/

LF Res Freq: 96.5
LF Res Q: 1.55
LF Resonance: 8.96

HF Res Freq: 1253
HF Resonance: 7.51
HF Slope: 2.9

 

[DrewJD82]

So are the takeaways that no 2 Rectos were ever created equal; and that low Master Volumes
on the Models in the Fractal are needed to more accurately approximate the behavior
of the Actual Amps themselves??

That and a dozen other things I probably am not smart enough to notice.

All ya need to know is we were right about the MV’s

 

[Mongillo19]

James Freeman is going to be the last gift on The Gift of Tone. It'll be a graph and code to make your own speaker curve

 

[la szum]

Haha! Master Volume behavior, accuracy, and matching (or differences) is something I think
a lot of us are interested in, and maybe have noticed some differences/discrepancies over the
years.

It's super interesting to me. I have found that most all of the amps I have owned, or have
experience, with need their Masters lower in the Fractalverse than with the actual amps.

With actual amps some of that power amp heavy lifting smooths out the preamp at higher MVs,
but with the Fractal I have found that higher MVs means the Fractal can cave in a little more
than the amp and I lose dynamics and headroom a LOT faster.

#menotthatsmart

I’ve been saying this for about 2 years!!!!!

 

[James Freeman]

LF Res Freq: 96.5
LF Res Q: 1.55
LF Resonance: 8.96

HF Res Freq: 1253
HF Resonance: 7.51
HF Slope: 2.9

Thank you!
Starting from the resistive load as the base?

 

[la szum]

All ya need to know is we were right about the MV’s

 

[MTB1973]

How I feel in this thread:

 

[Orvillain]

@FractalAudio one more question about the recto's - were they setup to use silicon diodes or tubes for rectification, and were they setup to use spongy or bold power modes?

 

[Elric]

Here's our OG Dual Rec into a real cabinet compared with the model into the appropriate SIC:

View attachment 15395

Green is the amp, blue is the Axe-Fx.

On the amp the MV is around 9 o'clock (as loud as I dared to go and not get divorced). I had to set the model to 1.2 to get the same response. Above that and the power amp starts clipping and the highs get reduced. This is to be expected given the different taper between the amp and the model.

While those curves clearly track really well overall, the general character of the amp's curve seems much more 'irregular' than the Axe... Is this telling us anything? Is that manifesting as something in realspace, ie. is this the 'smoothness' people claim to hear from the Axe vs a real amp?